The present disclosure generally relates to active solid-state devices, and more specifically to gallium nitride, high-electron-mobility transistors used as switches.
A gallium nitride (hereinafter “GaN”) high-electron-mobility transistor (hereinafter “HEMT”) is a depletion mode device (normally ON) that may be used as a switch. To turn the switch OFF, a gate needs to be biased at a negative voltage. Most applications do not have a negative voltage available on an application platform, thus the negative voltage needs to be generated from a smaller positive supply voltage. Generation of a negative voltage requires many stages of charge pump circuits. Each stage of a charge pump requires a capacitor. A size of the capacitor is dependent on a load current that the charge pump circuit has to source. The load current is a gate current of the HEMT device that the charge pump circuit is driving.
Modern applications demand that an RF switch handle high speed switching of high power RF signals, with high broadband isolation and low noise when the switch is OFF, and with low broadband insertion loss when the switch is ON. Every switch can have parasitic inductance, capacitance, conductance, and resistance. These parasitic components combine to attenuate and degrade the signal that the switch is being use to route. The power loss and voltage attenuation caused by these components varies with frequency of the input signal and can be affected by the insertion loss of the switch at that frequency. It is important that the insertion loss of a switch is acceptable at the bandwidth requirement of the application.
Many RF switches, such as PIN diode switches, suffer from high current drain. This can result in undesirable wasted power and generation of heat in certain applications.